So this has been bugging me for actual ages of mankind and now I have a place to ask. I recall that French authorities during the colonization of Algeria used as justification for imperialism the "regreening" of a desert back into a Roman cornucopia after many hundreds of years of mismanagement. Edward Gibbon points to the Berbers as being responsible during the wars against Uqba Ibn Nafi and the first big Muslim incursion into Algeria for "ruining" North Africa as a measure to deny the land to the Arabs.
I've also seen Romans themselves being blamed for it, or the Fatimids during the medieval period for "unleashing" a bedouin tribe and their goats upon the vulnerable soil, turning it into marginal scrub-land.
But none of these answers, besides being really scattershot and mostly not very well sourced, are very conclusive to me (at least from what I have).
So I thought I'd give it a go and ask you guys; Is North Africa significantly less fertile than it was in antiquity? If so, why?
Yes, it is. Before and during the Romans, many tribes/kingdoms were able to flourish in the Sahara which is much bigger than it was. During the Roman Empire, it was huge supplier of grain, along with fruits.
Rudimentary farming techniques have some impact on the fertility of the land (similar to Mesopotamia), but I do not know any other causes.